M2 The Immune System

Question 1

What are examples of non specific and specific defence mechanisms?

Answer 1

Non specific = physical barriers, phagocytosis

Specific = cell-mediated response, humoral response

Question 2

What is an antigen?

Answer 2

Any part of the organism/substance that is recognised as non-self (foreign) by the immune system and therefore stimulates an immune response.

Question 3

Where are antigens found? (what kind of cells?)

Answer 3

• cancer cells
• virus infected cells
• pathogens
• antigen presenting cells

Question 4

Describe the process of phagocytosis.

Answer 4

1) Phagocyte attracted to the pathogen by chemicals, going up the concentration gradient.
2) Pathogen binds to the receptors of the phagocyte.
3) The phagocyte engulfs the pathogen, forming a phagosome.
4) Lysosomes release lysozymes into the phagosome and pathogen is destroyed/hydrolysed.
5) Hydrolysis products are absorbed by phagocyte.
6) Phagocyte displays antigens of the pathogen on it’s cell surface membrane - becoming an antigen presenting cell.

Question 5

Describe the structure of antibodies.

Answer 5

Proteins made up of 4 polypeptide chains - quaternary structure - with 2 antigen binding sites. There are 2 light chains and 2 heavy chains (larger) with a variable region and a constant region. Receptor binding site at the bottom.

Question 6

What is agglutination?

Answer 6

The clumping of bacteria cells - increasing efficiency of phagocytosis.

Question 7

What do antibodies do?

Answer 7

They bind to the antigens of pathogens causing agglutination and stimulate phagocytes by acting as markers. Some may bind to toxins to prevent their action.

Question 8

What do antibodies form when they bind to antigens?

Answer 8

antigen-antibody complexes.

Question 9

B lymphocytes provide ______ immunity, T lymphocytes provide _____________ immunity.

Answer 9

Humoral

Cell-mediated

Question 10

What do T Helper cells do?

Answer 10

Their receptors bind to specific antigens on antigen presenting cells. They then divide rapidly by mitosis to form genetically identical clones of cells.

Question 11

What are the roles of clones of T Helper cells?

Answer 11

• Stimulate B lymphocytes to divide by mitosis.
• Become memory cells to carry out a secondary response to future infections.
• Activate cytotoxic T lymphocytes.

Question 12

What do cytotoxic T lymphocytes do?

Answer 12

They destroy harmful cells by secreting cytotoxic chemicals such as perforin, a protein that makes holes in cell membranes.

They destroy self-cells with foreign antigens.

Question 13

B lymphocytes provide ______ immunity by producing and _____ _______. There are approx. __ million different B cells and each is _____ to one antigen.

Answer 13

humoral  
secreting 
antibodies
10
specific

Question 14

What happens when a B lymphocyte encounters it’s specific antigen?

Answer 14

It engulfs the antigen by endocytosis and presents it on the cell surface membrane. T Helper cells attach to the antigens stimulating the cell to divide by mitosis to form clones which differentiate into plasma and memory cells.

Question 15

What is the name for antibodies which are specific to an antigen (produced by B cells)

Answer 15

Monoclonal antibodies

Question 16

Plasma cells ____ and secrete ________ - ______ immune response.
Memory cells are responsible for the _______ immune response.

Answer 16

produce
primary
secondary

Question 17

What is the name for the infection caused by animal pathogens that become adapted to human hosts

Answer 17

Zoonotic infections

Question 18

What are Pandemics caused by?

Answer 18

Antigenic shift in a pathogen so many people are not immune to it and so infection spreads rapidly within the global population.

Question 19

What is active and passive immunity?

Answer 19

Active = having memory B cells that are able to respond to a particular antigen and produce plasma cells that produce and secrete antibodies.

Passive = having antibodies that are able to bind to the antigen.

Question 20

Give examples of Natural and Artificial active immunity

Answer 20

Natural = Person naturally previously infected so has memory cells.

Artificial = Memory B cells present due to Vaccination

Question 21

Give examples of Natural and Artificial passive immunity

Answer 21

Natural = Antibodies transferred from mother to infant while breastfeeding.

Artificial = Antibodies transferred from one patient to another by plasma transfusion.

Question 22

What are the 3 types of vaccination?

Answer 22

Attenuated, live vaccine

Inactivated/dead vaccine

Virus-like vaccine

Question 23

HIV is a __________ - it contains _NA and _______ _________ (enzyme) which enables the virus to reproduce.

Answer 23

retrovirus
RNA
Reverse Transcriptase

Question 24

Describe the stages of replication of HIV

Answer 24

1) Attachment proteins on HIV bind to cell-surface receptors.
2) The lipid envelope of the HIV fuses with the cell surface membrane and the capsid is realised inside, where it ‘uncoats’ and releases RNA and enzymes.
3) Reverse transcriptase converts viral RNA to DNA.
4) The DNA moves to the nucleus and is inserted into the host cell’s DNA.
5) DNA is used to make mRNA using the host cell’s enzymes.
6) The mRNA acts as a viral genome - containing instructions to make the viral proteins using the host cell’s ribosomes.
7) Viral RNA and proteins are assembled into new viral particles that leave the cell, taking a piece of membrane with them that becomes the HIV lipid envelope.

Question 25

How does HIV cause AIDS?

Answer 25

Acquired Immune Deficiency Syndrome

• HIV kills or interferes with Helper T cells.
• AIDS is a collection of symptoms and illnesses- not a virus.

Question 26

What do antibiotics do?

Answer 26

Inhibit bacterial metabolic functions - e.g. cell wall synthesis, DNA replication, protein synthesis.

Question 27

Describe Direct and Indirect monoclonal antibody therapy for cancer.

Answer 27

Direct: antibodies bind to receptors on cancer cells, preventing growth factors from binding there - preventing uncontrolled division.

Indirect: Involves attaching radioactive or cytotoxic drugs to the monoclonal antibodies, which kill the cancer cells when they bind to their receptors.

These therapies are cheaper and have less side effects than radiotherapy/chemotherapy as they are only required in small doses.

Question 28

What does the direct ELISA test test for? How does it work?

Answer 28

Direct ELIZA = testing for the presence of antigen.

1) Antibody specific to the antigen of interest is bound to the surface.
2) Liquid sample added. If antigen is present it will bind to the antibodies.
3) Wash away unbound solution.
4) Second antibody added, complementary to the antigen, with enzyme attached.
5) Wash away unbound antibody.
6) Add substrate solution. If enzyme is present it converts it to a coloured product.

Question 29

What does the indirect ELISA test test for? How does it work?

Answer 29

Indirect ELISA = testing for the presence of antibodies.

1) Antigen bound to the surface.
2) Add blood serum. If antibody present it will bind to antigen.
3) Wash away unbound antibodies.
4) Add a second antibody, which is complementary to the patient’s antibody, with an enzyme attached.
5) Wash to remove unbound antibody.
6) Add substrate solution. If enzyme is present it converts it to a coloured product.